Add random colour to animations
You could create vertex-groups for each ring that should get another color when when hit by the character like this:



Assign each ring its own material with the same color at the beginning. When the character hits the background object determine which polygon has been hit by a technique described here:
How do I make a weapon shoot at the center of the screen? find the face hit by the character and set the material's color to a random color, this would change the color of faces (because all of the them share this material).